Process and a system for the production of sponge iron from iron ore

Abstract

A system for the production of sponge iron, including a direct reduction shaft, a reduction gas source, a reduction gas container, a primary circuit for conducting at least a part of a top gas therethrough, a secondary circuit for conducting at least a portion of gas removed from gas conducted through the primary circuit, said secondary circuit being connected in one end to the primary circuit and in another end to the reduction gas container, a second gas line connecting the reduction gas source with the reduction gas container, and a third gas line connecting the reduction gas container with the first gas line. The system also includes a control unit configured to control a flow of reduction gas from reduction gas source to the first gas line and to control a flow of reduction gas from the reduction gas container to the first gas line through the third gas line, wherein the control unit is configured to enable a flow of reduction gas from the reduction gas container to said first gas line while correspondingly reducing a flow rate of reduction gas from the reduction gas source to said first gas line.

1 . A process for the production of sponge iron from iron ore, the process comprising the steps of:
 charging iron ore into a direct reduction shaft;   introducing, via a first gas line, a hydrogen-rich reduction gas from a reduction gas source into the direct reduction shaft in order to reduce the iron ore and produce sponge iron;   removing a top gas from the direct reduction shaft, said top gas comprising unreacted hydrogen gas;   conducting in a primary circuit at least a part of the removed top gas and reintroducing said part of the top gas into the direct reduction shaft;   removing from said primary circuit a portion of the gas conducted therein, and conducting said portion of gas through a secondary circuit to a reduction gas container;   conducting reduction gas from the reduction gas source to said reduction gas container to form a gas mixture therein together with the gas from the secondary circuit; and   conducting the gas mixture from the reduction gas container to said first gas line and correspondingly reducing a flow rate of reduction gas from the reduction gas source to said first gas line.   
     
     
         2 . The process according to  claim 1 , wherein the step of conducting the gas mixture from the reduction gas container to said first gas line is a response to the gas pressure in the reduction gas container being above a predetermined level. 
     
     
         3 . The process according to  claim 1 , wherein the reduction gas source comprises an electrolyser driven by electric power, to which there is associated a fluctuating access-related parameter, wherein the process further comprises the step of continually registering the fluctuation of said access-related parameter, and wherein the step of conducting the gas mixture from the reduction gas container ( 209 ) to said gas line is a response to the access-related parameter being below a predetermined first level. 
     
     
         4 . The process according to  claim 3 , wherein the access-related parameter comprises any of a level of stored electric power in an electric power storage, an access-level of a means for generating the electric power, such as solar power, wind power or hydro power. 
     
     
         5 . The process according to  claim 1 , wherein the reduction gas source comprises an electrolyser driven by electric power provided via a public electric network, and wherein the step of conducting the gas mixture from the reduction gas container ( 209 ) to said first gas line ( 207 ) is a response to the load on the public network being above a predetermined level. 
     
     
         6 . The process according to  claim 3 , wherein reduction gas is conducted from the reduction gas source to the reduction gas container as a response to the access-related parameter being above a predetermined second level. 
     
     
         7 . The process according to  claim 1 , wherein said removal of said gas portion from the primary circuit to the secondary circuit is performed as a response to a pressure in the primary circuit being above a predetermined level. 
     
     
         8 . The process according to  claim 1 , wherein gas delivered via the secondary circuit and reduction gas delivered from the reduction gas source toward the reduction gas container is compressed in a compressor step before entering the reduction gas container. 
     
     
         9 . A system for the production of sponge iron, the system comprising:
 a direct reduction shaft comprising   a first inlet for introduction of iron ore into the shaft;   a first outlet for removing sponge iron from the shaft;   a second inlet for introduction of a reduction gas into the shaft, and   a second outlet for removing top gas from the shaft;   a reduction gas source connected through a first gas line with the reduction gas inlet;   a reduction gas container;   a primary circuit for conducting at least a part of the top gas therethrough, said primary circuit being connected in one end with the second outlet and in another end with said first gas line;   a secondary circuit for conducting at least a portion of gas removed from gas conducted through the primary circuit, said secondary circuit being connected in one end to the primary circuit and in another end to the reduction gas container;   a second gas line connecting the reduction gas source with the reduction gas container;   a third gas line connecting the reduction gas container with the first gas line; and   a control unit configured to control a flow of reduction gas from the reduction gas source to the first gas line and to control a flow of reduction gas from the reduction gas container to the first gas line through the third gas line, wherein the control unit is configured to enable a flow of reduction gas from the reduction gas container to said first gas line while correspondingly reducing a flow rate of reduction gas from the reduction gas source to said first gas line.   
     
     
         10 . The system according to  claim 9 , wherein the system comprises means for enabling a flow of reduction gas from the reduction gas container to the first gas line in response to the gas pressure in the reduction gas container being above a predetermined level. 
     
     
         11 . The system according to  claim 9 , wherein the reduction gas source comprises an electrolyser driven by electric power, to which there is associated a fluctuating access-related parameter, wherein the system further comprises means for continually registering the fluctuation of said access-related parameter, and wherein the control unit is configured to enable a flow of reduction gas from the reduction gas container to said first gas line in response to the access-related parameter being below a predetermined first level. 
     
     
         12 . The system according to  claim 11 , wherein the access-related parameter comprises any of a level of stored electric power in an electric power storage or an access-level of a means for generating the electric power, such as solar power, wind power or hydro power. 
     
     
         13 . The system according to  claim 9 , wherein the reduction gas source comprises an electrolyser driven by electric power provided via a public electric network, wherein the system comprises means for registering a load on the public electric network, and wherein the control unit is configured to enable a flow of the gas mixture from the reduction gas container to said gas line in response to the load on the public network being above a predetermined level. 
     
     
         14 . The system according to  claim 9 , wherein the control unit is configured to reduce an output of the reduction gas source in response to enablement of a reduction gas flow from the reduction gas container to the first gas line under the condition that a requested reduction gas flow in the first gas line is achieved. 
     
     
         15 . The system according to  claim 12 , wherein the control unit is configured to enable a flow of reduction gas from the reduction gas source to the reduction gas container in response to the access-related parameter being above a predetermined second level. 
     
     
         16 . The system according to  claim 9 , further comprises means configured to enable said removal of said gas portion from the primary circuit to the secondary circuit as a response to a pressure in the primary circuit being above a predetermined level. 
     
     
         17 . The system according to  claim 9 , wherein the system comprises a compressor arrangement for compressing said portion of gas delivered via the secondary circuit and reduction gas delivered from the reduction gas source through said second gas line before entering the reduction gas container. 
     
     
         18 . The system according to  claim 9 , further comprising at least one first sensor for measuring a reduction gas flow rate in the first gas line, at least one second sensor for measuring a temperature inside the direct reduction shaft, and at least one third sensor for measuring a pressure indicative of the pressure inside the direct reduction shaft, wherein the control unit is configured to determine a requested reduction gas flow rate in the first gas line and into the direct reduction shaft on basis of received input from said first, second and third sensors. 
     
     
         19 . The system according to  claim 9 , wherein the direct reduction shaft has a nominal production rate of sponge iron per hour, and wherein the storage capacity of the reduction gas container corresponds to the amount of hydrogen gas required for enabling reduction at said nominal reduction rate for at least one hour.